Derek answered questions like, "One of the four Kings' faces is different from the other three: which, and why?" But it was the final question that was the most amusing. Here's how the conversation went:

Host: "According to mathematicians at Harvard and Columbia, how many---"

Thank you for that Jack, bringing a big smile early on a Sunday morning.

Ronnie Barker and Ronnie Corbett (known in the UK as The Two Ronnies) once did a sketch based on the Mastermind quiz show, where contestants answered questions on their specialised subject. In this sketch, Corbett gives answers to the "question before last".